Birefringent component is widely used in many domains, such as polarized illumination system of immersion lithography, phase shifting interferometry and biological optics. The phase retardation and fast axis azimuth angle are two important parameters of birefringent component. The phase retardation distribution and fast axis azimuth angle distribution of the birefringent component must be acquired when it is used in the immersion lithography polarized illumination system and phase shifting interferometry. So it is of essentiality to precisely measure the phase retardation distribution and fast axis azimuth angle distribution of the birefringent component.
The Chinese Laid-Open Patent Application No. 200710178950.3 discloses a method and system of precisely measuring the optical phase retardation. By using an optical modulator in the optical setup, the modulated polarized light is generated. After filtering the measurement signals, the measurement of DC zero value is transferred to the measurement of AC zero value. By precisely judging the position of the extreme point, the phase retardation can be measured. But this method cannot measure the fast axis azimuth angle of the sample and the phase retardation distribution in real time.
Tsung-Chih Yu et al. in a paper entitled “Full-field and full-range sequential measurement of the slow axis angle and phase retardation of linear birefringent materials”, Applied Optics, Vol. 48, p. 4568(2009), discloses a method of measuring the phase retardation distribution and fast axis azimuth angle distribution of birefringent materials by using heterodyne interferometry method and three-step time-domain phase shifting method. This method needs to change part of the light path to measure the phase retardation distribution and fast axis azimuth angle distribution in step by step and uses the time-domain phase shifting technology, thus it is not feasible for measuring the phase retardation distribution and fast axis azimuth angle distribution in real time.